Update/Note: just to further clarify on the cheaters part since there are some people out there that are sending nasty tweets to Harada for the idea that PC players are all cheaters/hackers, he expressed in the tweet that there are many gamers out there that are one part of the overall community that do suspect PC players of cheating. Not necessarily himself that he thinks that all PC players are cheaters. He himself after all, is a big PC gamer.

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It's not a matter of the technology for getting the PS4/XB1/PC players to match up against each other being the issue, but rather first party company policies and potential security risks alongside the community perceived reputation of PC gamers being cheaters that is hindering the decision to allow cross platform play as explained by Tekken project leader Katsuhiro Harada on Twitter to a fan question.

That is not to say that cross platform play for the game has been outright denied however, merely that these hurdles are hampering the decisions to allow it. The specific usage of the home versions 'launch' in the explanation brings up an interesting consideration also by suggesting that all the drawbacks of allowing cross platform play can be avoided temporarily early in the game's lifespan and then later enabled to help the overall player base when the game has its 'drop off' of players. With that all said, there is a large possibility that cross-platform play for Tekken 7 will not be allowed when it launches in Early 2017 Harada says. If you yourself are passionate about the feature and its implementation in Tekken 7, why not let Harada know? He reads all the feedback he receives on Twitter.